Today, SpaceX recovered its Dragon spacecraft after a successful journey to the International Space Station — thus proving that a private company can transport supplies, or maybe even crew, to the ISS. Everybody's saying this is the real beginning of the era of private space travel.

But how much further could private companies like SpaceX take us? In particular, could they take us all the way to Mars? With NASA's budget constantly under fire, is there some way that a private corporation could fulfill our common dream of putting human beings on another planet? We decided to ask some experts and find out.

Top image: Painting by Ren Wicks for NASA.

Partnership with NASA

"If it wasn't for his interest in Mars, I don't think Elon Musk would do this," says Thomas Zurbuchen, Professor of Space Science and Aerospace Engineering at University of Michigan. Zurbuchen asked the SpaceX founder why he wanted to launch his own space company, and Musk responded, "I want to go to Mars," without blinking. That goal informs all of the design choices behind the Dragon, including using a much bigger launch vehicle than you'd need just to get cargo to the I.S.S.

That said, when people say that SpaceX proves that NASA's work is done and private companies can take it from here, they're exaggerating somewhat, says Linda Billings, a space policy analyst George Washington University. NASA still paid for the SpaceX launch, and we don't actually know how much it really cost:

While SpaceX is working for NASA under a different sort of contractual agreement than the previous crop of launch companies, it remains to be seen whether NASA, and thus the taxpayers, will be saving any money on space flight. It is difficult to find out from NASA exactly how much money it has spent on the new crop of so-called commercial launch companies, including straight-out subsidies.

She also points out that private companies have built every NASA vehicle since the Saturn V rocket, so the notion of NASA collaborating with private companies is not exactly new.

"I have to say, I'm a skeptic as to how far private space operations can take us right now, in terms of commercializing space," says Andy Turnage, executive director of the Association of Space Explorers. Of course, the industrial capacity of the United States wasn't built overnight either, and there's no telling how commercial space operations will develop over time. Even Musk probably wouldn't say that a trip to Mars makes sense from a strict business standpoint right now, adds Chris Carberry, executive director of Explore Mars, Inc.

The only way to do things like a trip to Mars is a private-public partnership, insists Zurbuchen. "I believe that the entrepreneurial spirit of big companies and enterprises is crucial to big ventures." On its own, government-funded science tends not to have a goal beyond pure exploration, and "all you want to do is learn, learn, learn." Meanwhile, a private company that's just out to make a quick profit won't do a big thing like going to another planet. "Whenever you reach far, it's tough to make a business case." Image from Mission to Mars.

But when you combine the drive for exploration with an entrepreneurial spirit, "this is what drives the world forward," says Zurbuchen. It would be a better world if these two strands were combined more often.

What's most likely to happen is that companies like SpaceX will "take the burden" of getting people into Low Earth Orbit (LEO) off of NASA — freeing up NASA to spend its time and resources on new missions such as getting people to Mars, says Lt. Col. Paul Damphousse, executive director of the National Space Society. We've been putting people into LEO for 50 years now, and there's no reason for NASA to keep doing it.

If private enterprise can deal with the problem of getting people into LEO, then "government can tackle the things that private industry cannot do itself or does not want to do itself," says Damphousse. "Government will help to buy down the risk and prove the technology so that at some point in the future private enterprise can step in and take over just as they're going to do with Low Earth Orbit."

But what if NASA never manages to get the funding to send people to Mars? Could a private enterprise be the one to get us there in the next couple decades instead? It may depend on finding a business rationale, and making it cheap enough.

How a Trip to Mars Could Pay

When Zurbuchen says "it's tough to make a business case" for going to Mars, he's kind of understating things. How could a private entrepreneur possibly justify such a fabulously expensive venture as a canny investment?

But there are many different ways you could possibly justify a trip to Mars from a pure business standpoint, if you're willing to make a huge outlay for a big return down the line. Here are some of the things people suggested to us as possible ways to get a return on your investment:

Bragging Rights: "How much money would you be willing to spend to have your name go down in history as the first person to step on Mars?" asks Turnage. This is a kind of immortality whose value could be incalculable. And, at least for now, Turnage believes it's the only way to justify spending money to go to Mars from a strict financial standpoint. Image by Pat Rawling/NASA.

Tourism: Mars could be the ultimate "high-end destination," says Zurbuchen. Rich people might pay tons of money to have a vacation there. "It could be that that makes sense in the future."

Mining: It's possible that Mars will turn out to have valuable minerals or radioactive elements, that are worth going there to mine, says Zurbuchen. On the other hand, Turnage points out that to make this a return on someone's investment, you have to spend the money to ship that stuff back to Earth, "to do something with it here." We don't know enough about the resources available on Mars yet, to know whether there's anything worth shipping back to Earth, but if it's valuable enough, then someone will find a way.

The real question is, could you find any resources on Mars that you couldn't also find on an asteroid?, says futurist Jamais Cascio with Open the Future. There are probably enough gold and other rare minerals on one big "iron" asteroid to crash global markets forever — but what can you find on Mars that you can't find on asteroids, which don't have their own gravity wells? At least for now, Mars isn't known to have anything particularly useful — or unique.

Drug discovery: If Mars turns out to have life on it, then all bets are off, says Cascio. "There's good reason to suspect that Martian life will actually resemble Earth life (in short, pretty good likelihood that early Earth life got blasted off-world by a big asteroid strike, with some of it potentially getting to Mars — or, even better, Mars getting developing life first (smaller planet=cools faster), and having Martian life blasted off to hit Earth, kick-starting life here!), or could at least be similar enough to prompt new lines of bio research. Being able to patent the genes of a non-Earth species would be worth some big money."

Reality TV: Given how long a trip to and from Mars would be likely to take, and the immense potential for personal drama, you might be able to get people back on Earth to watch a TV show about the first humans going to Mars. Although eventually, viewer interest might drop off — leading to cancellation, which could leave these first Martian visitors stranded forever.

How to Make it Cheap Enough

Proponents of privately funded space exploration say that ventures like SpaceX are going to bring down the costs of space travel through innovation, and that in turn will lead to huge advances in space travel without any need for government involvement. But when it comes to a trip to Mars, the costs are still likely to be enormous.

According to Carberry with Explore Mars, estimates of the costs of a NASA trip to Mars have ranged from $150 billion to $1 trillion. Robert Zubrin has estimated a private venture to go to Mars might only cost $4 to $6 billion. And Elon Musk himself told Carberry that he thinks it can be done for just $2 billion, although Carberry says that estimate is probably not built on any detailed numbers. Image via Mars Society.

There are two huge reasons a trip to Mars is so expensive, says Damphousse: escaping Earth's gravity, and then keeping people alive on the long trip to Mars. How do you go about making both of those things cheaper, and how could private companies make a difference in those areas?

Getting into space:

There's no getting away from it, just getting off our planet is a huge, massive expense. Carberry says the launch vehicles for NASA's Space Shuttles cost $10,000 per pound of cargo. But the good news is, SpaceX's first launch to the I.S.S. already "cost a fraction of what it would have cost through the traditional NASA process," says Carberry. If SpaceX can make getting into LEO both cheap and reliable, and increase the frequency of flights into LEO, then we'll have helped to solve one big piece of the "getting to Mars" problem, says Damphousse.

Carberry says there are two big questions: whether SpaceX can get its Dragon capsule rated for human crews, while still keeping costs low. And whether SpaceX can grow without its currently low overhead ballooning.

But bear in mind that getting into LEO, as SpaceX did, is not the same thing as getting out of Earth's gravity well entirely, Cascio points out:

Getting out of Earth's gravity well entirely (to go to the Moon or Mars) would take considerably more launch power. It's said that we no longer have the capacity to build a Saturn V (the only rocket ever built able to get a human out of the Earth's gravity well), and while that's really just a matter of tooling up the right kinds of factories, it still suggests that the costs of building a comparable vehicle now would be ridiculously high, especially compared to the relatively cheap low-Earth orbit launch vehicles.

Any private company that is serious about going to Mars is probably going to want to invest in creating a space elevator first, says Cascio. That way, you can use the space elevator to launch satellites and other things into orbit, thus helping to pay off the costs. And you've already massively reduced the costs of launching your Mars vehicle.

Getting to Mars:

The good news is, once you've gotten out of Earth's gravity well, the costs of travel drop considerably, says Cascio:

You retain all of your momentum, can use gravity-assist "slingshots," and only need rockets for maneuvering. That's why getting to the asteroids will be much easier than getting to the Martian surface, at least if you plan to return from Mars — the asteroids are essentially a zero-G environment. And that, incidentally, is why some of the realistic plans for a Mars mission describe it as a one-way trip, sending a group of astronauts there to become colonists.

Another piece of good news is, your hypothetical Martian exploration vessel might not need to carry supplies for the crew to survive on Mars, or for the return trip, says Carberry. We may be able to make oxygen and methane fuel using the water on Mars, or else by converting Mars' CO2 atmosphere using our own hydrogen. "One of the key ways to keep costs down is to keep the mass of the mission down," says Carberry. "If you can manufacture your supplies on the surface of the planet, you can cut down the mass of the mission."

Adds Cascio, "many of the more realistic plans for Mars exploration, such as [Robert] Zubrin's, involve sending automated vehicles there first to gather materials to produce fuel in situ for the return flight."

One piece of bad news, though: the biggest expense of going to Mars could be just finding ways to keep "monkeys alive in aluminum cans, while in a high-radiation environment," says Cascio. Compared to just three days each way for a Moon trip, the weeks or months required to go to Mars mean massively more radiation shielding — which means more weight, which means more cost. Image: Paul Hudson for NASA

Both NASA and several private companies are working on "in-space technologies" that could make the flight to Mars cheaper and easier, says Damphousse: "Things like advanced robotics, cryogenic propellant storage and transfer, and solar electric propulsion are just a few examples of very low cost things that we could do, that enable what I call mission multiplers, that allow us to do things better in space."

Also, people are working on advanced propulsion systems that could get people to Mars much faster, thus reducing the amount of fuel you need to use — and also cutting down on radiation exposure and bone loss. Companies like Franklin Chang-Díaz's Ad Astra Rocket Company are trying to develop much faster propulsion systems, says Carberry, but it's not clear if these will ever be useable for human exploration.

If we actually manage to get people to Mars and they survive the trip, that means we'll have solved "a heck of a lot of problems" that could make the world a better place in general, says Zurbuchen. We'll have figured out the answers to a lot of major questions, and probably increased the living standards of people on Earth in the process.